Step-down transformers have been used for many years as electrical power was harnessed in manufacturing processes. Such transformers are often used to reduce a line voltage associated with a main power supply in an industrial application to levels applicable to equipment connected to an output side of the transformer. In the United States, it is common to step down a main power supply of 480 volts down to about 120 volts, which is the voltage required for powering numerous accessories such as lights, electric hand tools, instruments, mini-computers, inspection lamps, and the like.
In the design of a large machine tool, machine device, or machine system in an industrial setting, the need frequently arises for auxiliary power to be available when the main power supply is disconnected or turned off. The auxiliary power may then be used to furnish a supply of secondary, stepped-down electrical power to the associated accessories. Devices designed to provide such auxiliary power are commonly referred to as auxiliary power supplies or lighting disconnects. Their application is found extensively in machines and machine tools used in the automotive industry, as well as other industries.
Auxiliary power supplies, including transformer assemblies, have been manufactured and used for some time. They generally include a container into which, for example, a transformer, fuses, wiring, and terminal boards are placed. A rotary or other type of switch is generally installed in the container with a handle extending through the container. In operation, if a cover of the container is opened, power from the auxiliary power supply is disconnected in much the same way as power is interrupted by the opening of doors on a main panel associated with the main power supply.
However, auxiliary power supplies available in the past leave unsolved the problem of bulk because they can be accommodated only with difficulty within the scarce space which is available in typical machine tool control panels. The layout of machine tools, machines, and industrial processing equipment frequently includes control panels within which are accommodated auxiliary power supplies. Often, the machine designer has difficulty in finding a place to install the auxiliary power supply, even though specified by a customer. This is because panel space is expensive and the plethora of increasingly complicated devices which must be contained within the control panel compete for the scarce amount of space available. There is therefore an unmet need for an auxiliary power supply which is smaller, more compact, and more useful than the devices generally available in the past. It would therefore be useful to have an auxiliary power supply which is small and compact, thereby facilitating its accommodation in the complex machine tool environment.
Under traditional approaches such as described above, auxiliary power supplies are mounted within the container which is located in the confines of the machine tool control panel. This configuration generates heat which is difficult to dissipate because of the proximity of numerous electrical components outside and within the container. As a result, ambient temperatures rise, the electrical integrity of various components becomes jeopardized, and eventually any insulation system associated with the transformer assembly begins to break down. A need has therefore arisen for a transformer assembly which, besides being compact, is so constructed that heat may readily be dissipated from exposed portions of a core so that operating temperatures are maintained within acceptable limits.
Conventionally, in addition to the transformer, a number of electrical components such as receptacles, fuses, switches, and the like are mounted at least partially within the container which envelopes the transformer assembly. Besides requiring a relatively large amount of space within the control panel in the machine tool environment, conventional configurations do not allow ready dissipation of heat because of confinement by the container of the transformer assembly. To solve this problem, it would be desirable to dispense with the container and its associated electrical components and have a stand-alone transformer assembly including hollow housings mounted on an exposed core, the housing including electrical components mounted at least partially within at least one housing. In this way, the space occupied by the transformer assembly is kept to a minimal amount, while providing for ready dissipation of heat by the exposed portions of the core.
The concept of attaching a hollow housing over exposed coils and wiring associated with input and output requirements of the transformer have been known for many years. Illustrative is U.S. Pat. No. 3,810,057 issued to Franz, et al. Many transformer manufacturers offer standard models with end covers or caps. Such covers are cup-like shaped objects which extend from the core of a transformer around the exposed coils and associated wiring. However, such approaches usually involve the end caps covering at least part of the core, thereby leaving unsolved the problems and adverse consequences of heat build-up due to ineffective cooling of the coils of the transformer.
It is well known that potentially damaging types of line disturbances in main power supplies fall into one or more categories. Impulses, for example, characteristically last for a short time and may be accompanied by fast swings in voltage. Such disturbances have been found to cause a large percentage of computer data errors and can cause equipment malfunctions. Additionally, sags and surges can generally be described as short duration changes in voltage levels which occur due to sudden changes in the demand for power. Such phenomena contribute to computer error and other equipment malfunction. Also, brownouts, or changes in voltage from a nominal level may last for significant periods. As a result, computers may suffer data errors or memory loss, and electrical devices may overheat or operate inefficiently. To meet such difficulties, there is increasing awareness of a need for transformer assemblies with the attributes described above and which will mute or eliminate power line disturbances.
In industrial situations where programmable controllers are used, unique power requirements must be met. Such controllers may call for a particular wave shape and voltage regulation with minimal harmonic distortion. To meet such requirements, constant voltage transformers have been utilized to provide highly regulated outputs with low harmonic distortion. Ideally, such transformers can maintain the correct output voltage within a fairly narrow range for input variation which may be significant. Accordingly, there has arisen a need for constant voltage transformers which satisfy particular operating requirements within compact dimensional constraints, and which still exhibit other attributes demanded by complex machine tool environments.